Current research focuses on the pathogenesis of Mycobacterium. The closely related N. asteroides is emerging as an important pathogen in patients with immunodeficiencies and in healthy people; yet, Nocardia species have received little research attention. N. asteroides GUH-2 (GUH-2) is an ideal model for research because its pathogenesis has been studied extensively both in vivo and in vitro. It produces substances important for differential adherence to and invasion of the lungs and brain, alteration of phagocyte function, abrogation of microbicidal activities of phagocytes, and cellular cytotoxicity. The molecular and genetic mechanisms which control these activities are not known. Our hypothesis is that filament tip associated proteins on the surface of log phase organisms adhere selectively to surface receptors and trigger invasion by the induction of a particular signaling process within these host cells. The following specific aims are proposed to test this hypothesis: (1) To determine the filament tip associated proteins involved in differential adherence to specific host cell surfaces, and identify the genes that encode for these surface proteins. (2) To determine whether these filament tip proteins facilitate invasion and dissemination. To achieve these goals, filament tip associated proteins of GUH-2 that bind to the surface of host cells, promote invasion, and dissemination will be determined. The genes which encode for these substances will be identified, cloned, sequenced and expressed in either N. asteroides GUH-2, N. lactamdurans, or E. coli. Adherence and invasion of these recombinants will be studied in vitro and in vivo by biochemical, immunological, light and electron microscopic, and microbiological methods. This will identify components involved in adherence to and invasion of host cells resulting in an understanding of mechanisms for organ specificity and dissemination. These studies should lead to improved diagnosis, treatment, and prevention of nocardiosis.